1. Field of the Invention
The present invention relates to a spreading and lap-forming machine for converting a web to a lap by folding in pleats.
2. Description of the Prior Art
In a machine of this type as disclosed, for example, in patent document FR-B-2,553,102, a web delivered by a card is first conveyed by a first conveyor-belt or so-called front belt to a pinching zone in which it is maintained between the first belt and a second belt and conveyed to an output carriage. The reciprocating motion of the output carriage above a receiving apron causes deposition of the web which said carriage discharges onto the apron in alternate accordion pleats. Since the apron moves in a direction parallel to the axes of the guide rollers carried by the output carriage, the successive pleats are relatively displaced along this direction and the web thus forms on the apron a continuous lap, the lateral edges of which are defined by the pleats. The beginning of the pinching zone is defined as a position in motion by an input carriage which performs a reciprocating movement. This movement is intended to ensure that the speed of admission of the web into the spreading machine is made compatible with the speed of unwinding of the web by the output carriage in spite of the reciprocating movements of said carriage. Thus the web, which has a fragile structure, is not disturbed either by packing or by stretching or by friction.
In machines of this type, the developed length of the closed paths followed by the conveyor-belts must be maintained constant in spite of the reciprocating movements of the carriages.
In some designs, the reciprocating motion of the input carriage is compensated by the contrary reciprocating motion of the output carriage and conversely by means of a suitable arrangement of the guide rollers (reference can be made, for example, to patent document FR-B-2,553,102).
In other designs (see FR-B-2,234, 395, U.S. Pat. No. 1,886,919 or FR-A-2,373,095), provision is made for one or a number of auxiliary carriages which also carry out reciprocating movements of translation in order to selectively lengthen or shorten the conveyor-belts outside the pinching zone and thus to compensate for variations in length of the pinching zone.
The present Application is more particularly concerned with this second type of construction.
It has been found that spreading and lap-forming machines of this type give rise to difficulties when they operate at the high speeds which may be desired in order to increase production rates. The alternating motion of the auxiliary carriages in that case produces relatively violent air currents which tend to disperse the web conveyed on the front belt upstream of the input carriage. This may result in defects in homogeneity of the lap produced and even in jamming of the web in the pinching zone.
In the spreading and lap-forming device described in patent document U.S. Pat. No. 1,886,919, the auxiliary carriages are slidably mounted within the closed loop described by the apron which receives the lap. Their reciprocating movements therefore produce air currents in the vicinity of the lap deposited on the apron, with the result that this spreading and lap-forming device cannot produce a uniform lap at relatively high speeds.
In the spreading and lap-forming device described in patent document FR-A-2,373,095, the auxiliary carriage moves above the input carriage. This structure reduces the disturbing effect of the movement of the auxiliary carriage on the formed lap in comparison with U.S. Pat. No. 1,886,919. However, this disturbing effect is in fact exerted on the web which is supplied to the input of the machine. This results in the same disadvantage: uniformity of the lap formed at the exit of the spreading machine is poor, particularly at high speed.
One of the objects of the present invention is to solve these difficulties and to provide a spreading and lap-forming machine which produces a uniform lap, even at high speed.